Higher-order gradient effects in micropillar compression

Deformation behavior in single-slip oriented micropillars subjected to compressive loading is analyzed using a three-dimensional finite element method incorporating a higher-order gradient crystal plasticity theory in which the spatial gradients of the geometrically necessary dislocation densities are assumed to give rise to backstress that impedes or promotes dislocation motion, depending on its sign. In experimental studies, it has been frequently observed that the gauge portion of micropillar samples is split into a shear zone and two nearly unstrained dead zones under compressive loading. Here it is shown that effects of a higher-order gradient are essential for the formation of this particular deformation mode.